TVK alla conferenza EASC 2009

Optimisation of reed valves dynamics by means of Fluid Structure Interaction


In this study the dynamic of a six petals reed valves pack is simulated accounting the complex fluid interaction phenomena occurring during transient flow of a working cycle typical for a two-stroke engines for go-kart competition. Starting from previous works by the same research group related to reed valve FSI simulation for 2D problem and to the optimization of valve material considering only the structural 3D dynamic, this new step has been made possible thanks to a further developing of a dedicated approach. Technically speaking, the proposed approach consists in the use of Fluent and an embedded FSI tool. The tool is based on a suite of UDF functions that allows to generate a structural model conform to the boundary of the fluid mesh, exchange information between the models (pressure and displacements through a weak approach on a time step basis or inside the non-linear iteration), solve the structural part by FEM adopting a general shell element and accounting for non linearity (contact in this case). Case definition for the coupled problem is fully integrated in fluent by means of a GUI and a TUI written in scheme language.
Study of reed valve opening under steady boundary condition (considering the transient of fluid during valve opening) is presented.




Optimisation of motorbike windshield by means of morphing


In this paper the aerodynamic optimisation of a motorbike windshield is presented. The aim of the study is the comparison between the original touring windshield and an aftermarket variotouring windshield. The latter is composed by a fixed part and an adjustable spoiler and allows to accommodate different driver heights.
A complete design loop has been defined with the aim to establish a fast method to introduce a new product at the first presentation of the motorbike model. The design loop consists in the acquisition of the actual geometry of part of the motorbike by means of a reverse engineering tool, the definition of the new windshield geometry, the introduction of the driver in the CAD model, the definition of the calculation mesh, the CFD model of the baseline geometry (one with the original windshield and another one with the new component), the shape optimisation of the new geometry.
The optimisation goals are the vehicle drag and driver comfort, the latter can be addressed evaluating the resultant of aerodynamic actions on the helmet. Considering that the windshield is adjustable, an optimal angle can be found for the driver height, for this reason design optimisation becomes a multiobjective problem because design parameters (i.e. shape of the two parts of varioutouring) affects how the component will perform for different drivers.
This challenging optimisation task was made possible tanks to Fluent and an embedded morpher tool capable to modify the baseline mesh accounting both for set-up changing (i. driver height and spoiler angle) and shape changing (i.e. the shape of the spoiler and the fixed part).
The tool is based on a suite of UDF functions that allows to prescribe surface modifications, smooth accordingly the volume mesh preserving the quality, update the solution. The morpher is meshless (i.e. is defined using only a set of points and produces a deformation field) and can be used both in serial and parallel sessions allowing to manage any kind of mesh because it acts only on node positions. Morphing set-up is done inside Fluent thanks to a powerful GUI that allows to define the problem interacting with Fluent entities, TUI commands are also available that allows to modify the shape by means of simple scripts.

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